1,721,662 research outputs found
AN INTEGRATION OF HEURISTIC AND MODEL-BASED REASONING IN FAULT-DIAGNOSIS
No full textA human expert utilizes various pieces of diagnostic knowledge very dynamically in problem solving. Recently a few integrated reasoning systems have been proposed to use various types of knowledge in an integrated way, but they have shortcomings in reasoning control and reasoning interactions. To overcome these shortcomings, a diagnostic reasoning system with dynamic interactions that uses diverse types of knowledge with cooperation is proposed. The integrated diagnostic reasoning system contains heuristic and model-based reasoning modes. A type of knowledge in one reasoning mode is shared with another via transformation knowledge. In the integrated diagnostic reasoning system, the heuristic reasoning mode plays a major role in reasoning, and the model-based one fills the gaps in the heuristic reasoning mode. The model-based reasoning mode helps the heuristic one by supporting primitive-level testing, and by generating symptoms and hypotheses. In addition, it undertakes the remaining tasks if the heuristic reasoning mode fails. The heuristic reasoning mode, also, aids the model-based one by pruning the candidate set. By applying the integrated reasoning system to diagnosis of a computer printer circuit the system is shown to be appropriate for the domain that calls for the cooperative use of heuristic and detailed system description knowledge. With the criteria of efficiency and coverage, it has been shown that the proposed system is appropriate when insufficient symptoms and heuristic rules are provided
Choice of approximator and design of penalty function for an approximate dynamic programming based control approach
No full textThis paper investigates the choice of function approximator for an approximate dynamic programming (ADP) based control strategy. The ADP strategy allows the user to derive an improved control policy given a simulation model and some starting control policy (or alternatively, closed-loop identification data), while circumventing the 'curse-of-dimensionality' of the traditional dynamic programming approach. In ADP, one fits a function approximator to state vs. 'cost-to-go' data and solves the Bellman equation with the approximator in an iterative manner. A proper choice and design of function approximator is critical for convergence of the iteration and the quality of final learned control policy, because an approximation error can grow quickly in the loop of optimization and function approximation. Typical classes of approximators used in related approaches are parameterized global approximators (e.g. artificial neural networks) and nonparametric local averagers (e.g. k-nearest neighbor). In this paper, we assert on the basis of some case studies and a theoretical result that a certain type of local averagers should be preferred over global approximators as the former ensures monotonic convergence of the iteration. However, a converged cost-to-go function does not necessarily lead to a stable control policy on-line due to the problem of over-extrapolation. To cope with this difficulty, we propose that a penalty term be included in the objective function in each minimization to discourage the optimizer from finding a solution in the regions of state space where the local data density is inadequately low. A nonparametric density estimator, which can be naturally combined with a local averager, is employed for this purpose. (c) 2005 Elsevier Ltd. All rights reserved
Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on particle formation
No full textThe emulsion polymerization of TFE was carried out with a surfactant (FC-143) and an initiator (ammonium persulfate) under various reaction conditions. Two different shapes of PTFE dispersion particles were produced by the emulsion polymerization, rods and spherical particles. Variables, except for surfactant concentration, do not affect the initial and final particle morphology when no coagulation occurs. Rod-like particles are formed when the surfactant concentration is near or above the critical micelle concentration (CMC) of the surfactant. At below CMC, however, spherical particles are dominant. No hexagon-shaped particles or abrupt changes in the particle morphology are observed during polymerization. When no coagulation occurred, the size and number of polymer particles suddenly increased in the early stages of emulsion polymerization and then steadily increased as time progressed. Most particles are formed in the early stages (within 5 min), and the size of particles formed was in the range 60-80 nm in diameter. The particle sizes ranged from 100 to 230 nm at 250 g/l of a specific TFE uptake concentration (the PTFE dispersion had a solid content of about 20%). It was found that the size and number of polymer particles formed are almost independent of the temperature, pressure, concentration of initiator and stabilizer (anti-coagulant), whereas the surfactant concentration, kinds of stabilizer, and agitation speed are important. The particle size decreased gradually as the dispersion concentration increased, whereas the particle number increased exponentially. When the PTFE dispersion coagulated during polymerization under certain conditions (high temperature and agitation speed, and low concentration of surfactant), the particle size suddenly increased, the particle number suddenly decreased, and the rate of the polymerization decreased, indicating that the polymerization occurred on the surface of the polymer particles. (C) 1999 Elsevier Science S.A. All rights reserved
Diode-pumped femtosecond Nd:glass fiber laser started with a moving mirror
No full textThe start-up of passive mode-locking with a moving mirror was demonstrated in a Nd:glass fiber laser pumped by a single-stripe laser diode and pulses with a duration of 250 fs were generated. A relatively long fiber was used to lower the mode-locking threshold by increasing the Kerr effect in the fiber and the variation of the threshold for the start-up of mode-locking was investigated by changing the length of the fiber from 0.74 to 2 m., It was found that the restriction of the lasing spectrum using an intracavity slit was crucial for a low start-up threshold of mode-locking in a Nd:glass fiber laser
Call arrival history-based strategy: Adaptive location tracking in personal communication networks
No full textIn this paper, we propose a call arrival history-based location tracking strategy for a variable call arrival rate over Lime. The basis of the proposed strategy is a time-based location tracking strategy. A mobile terminal obtains the up-to-date information about changes in the call arrival rate by maintaining its call arrival history, from which it can calculate an appropriate timeout interval for a variable call arrival rate. We present a simple analytical model and numerical results to investigate its performance for both a fixed and a variable call arrival rate which is modeled by a Markov-modulated Poisson process
Catalytic coal gasification in an internally circulating fluidized bed reactor with draft tube
No full textAustralian subbituminous coal loaded with the single and mixed catalysts of the alkali and transition metal salts [K2CO3, Ni(NO3)(2), K2SO4, Ni(NO3)(2 +) K2SO4] was gasified in an internally circulating fluidized bed (0.3 m-I.D. x 2.7 m-high) with a draft tube (0.1 m-ID x 0.9 m-high) at atmospheric pressure. Air and steam as the reactant gases were introduced into the draft tube and annulus regions in the bed separately. The effects of reaction temperature (750-900 degrees C), O-2/coal ratio (0.3-0.5) and steam/ coal ratio (0.3-0.8) on compositions, gas yield, calorific value of the product gas, and carbon conversion in the catalytic and non-catalytic coal gasifications have been determined. Coal gasification in the newly developed internally circulating fluidized bed with a draft tube produces higher calorific value gas (12 MJ/m(3)) with higher catalytic reaction rate and selectivity compared with the other types of gasifiers. (C) 1998 Elsevier Science Ltd. All rights reserved.the Ministry of Trade, Commerce and Energy, Kore
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Emulsion polymerization of tetrafluoroethylene: Effects of reaction conditions on the polymerization rate and polymer molecular weight
No full textThe emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles, Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 X 10(-3) and 32.48 X 10(-3) mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. (C) 1999 John Wiley & Sons, Inc
Hydrogen Bond-Directed Stereoselective Synthesis of Z-Enamides via Catalytic Olefination Reactions of Primary Amides
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